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Commitments and Contingent Liabilities - Notional Amount of Outstanding Commitments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Commitments to extend credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 1,519,436	$ 1,571,987
Financial standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	37,119	38,121
Performance standby letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	27,458	32,441
Commercial letters of credit [Member]
Loss Contingencies [Line Items]
Financial instrument of credit risk	$ 0	$ 0

X

- Definition

Notional amount of outstanding commitments and letters of credit.

+ References

No definition available.

+ Details

Name:	fcf_NotionalAmountOfCommitmentsAndLettersOfCredit
Namespace Prefix:	fcf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration